This invention relates to an electrostatic chuck having improved erosion resistance for holding a substrate in a process chamber.
In semiconductor fabrication processes, electrostatic chucks are used to hold substrates, such as silicon wafers, during processing of the substrate. A typical electrostatic chuck comprises a base adapted to be secured to a support in a process chamber. An insulator with an electrode therein is on the base. An electrical connector electrically connects the electrode in the insulator to a voltage supply source. Electrostatic chucks are generally described in, for example, U.S. Pat. No. 4,184,188, to Briglia; U.S. Pat. No. 4,399,016, to Tokuda; U.S. Pat. No. 4,384,918, to Abe; and U.S. patent application Ser. No. 08/189,562, entitled "Electrostatic Chuck" by Shamouilian, et al., filed on Jan. 31, 1994--all of which are incorporated herein by reference.
To use the chuck, a substrate is placed on the chuck, and the insulated electrode on the chuck is electrically biased with respect to the substrate by a voltage applied via the electrical contact of the chuck. The applied voltage causes electrostatic charge to accumulate in the electrode of the chuck and in the substrate and the resultant electrostatic force holds the substrate to the chuck.
The insulator on the chuck typically comprises an insulative polymer, such as polyimide. The use of polymers to insulate the electrode of the chuck, limits the lifetime of the chuck in corrosive semiconductor fabrication processes, particular in processes which use oxygen containing gases and plasmas. Oxygen containing gases and plasmas are used for a variety of tasks, including etching of substrates, and cleaning of process chamber walls. These corrosive environments rapidly erode the polymeric insulator on the chuck.
Erosion of the insulator on the chuck results in failure of the chuck. Although a large portion of the insulator on the chuck is protected from the corrosive environments by the substrate held on the chuck, portions of the insulator which are exposed to the corrosive gases can erode in as few as a thousand process cycles. For example, when a substrate is electrostatically held on the chuck, the peripheral portion of the insulator is typically exposed to the corrosive environment in the process chamber. The corrosive gases in the chamber rapidly erode the exposed peripheral insulator portion. Erosion of the insulator at even a single point is sufficient to cause arcing of the electrode therein, requiring replacement of the entire chuck. Frequent replacement of the chuck is expensive and slows down the fabrication process. Also, if the chuck fails during processing of the substrate, the entire substrate can be lost, at a cost of several thousands of dollars.
Although alternative insulative materials, such as silicon oxide based insulators, can be used to protect the electrodes in oxygen containing processes, these materials have other inherent limitations. For example, silicon oxide based insulators rapidly erode in processes that use fluorine containing gases, such as fluorocarbon gases. Also, the silicon oxide based insulators are more difficult and expensive to manufacture.
Thus, it is desirable to have electrostatic chuck that is substantially resistant to erosion in corrosive gaseous environments containing gases. It is further desirable to have a chuck that can be inexpensively fabricated using conventional fabrication equipment.